Numerous electronic tuning devices have been proposed for aiding a musician in the tuning of a musical instrument. In operation, these devices generally fall into three broad categories.
Devices in the first category use a microphone, pick-up, or other transducer to convert an acoustic tone from a musical instrument into an electrical signal which is analysed using various means, ultimately displaying with a meter or other electronic display, whether the tone is sharp, flat, or in tune. Examples of this type of device include U.S. Pat. Nos. 3,631,756 issued to Mackworth-Young in May 1968; 4,028,985 issued to Merritt in June 1977; 4,688,464 issued to Gibson in August 1987; and 5,637,820 issued to Wittman in June 1997.
Devices in the second category use a transducer to convert an acoustic tone into an electrical signal which modulates the overall perceived brightness of a display, such as a rotating painted disk or a circle of light emitting diodes (LEDs), which rotates, flashes, or otherwise changes in a periodic manner at the frequency of a desired tone. The well-known stroboscopic effect creates an illusion to the human eye of movement of the display which appears to slow down and stop as the instrument is brought into tune. Examples of this type of device include U.S. Pat. Nos. 3,861,266 issued to Whitaker on Jan. 21, 1975; 3,952,625 issued to Peterson on Feb. 18, 1975; 5,016,515 issued to Scott on May 21, 1991; and 4,252,048 issued to Pogoda on Feb. 24, 1981.
The above devices in the first and second category suffer from the use of a transducer or input from a transducer. A transducer adds complexity and expense. In addition, many of the designs recognize that extraneous noise and other errors in the input signal are problematic. In most devices, the musician must take care to sound only one string at a time while tuning.
In the third category, the devices have the advantage that they do not use a transducer, but rely instead on the directly observable physical vibration of the vibrating part of a musical instrument, such as the string of a guitar. Stroboscopic illumination is used to slow down and stop the apparent vibration as the instrument is brought into tune. U.S. Pat. No. 3,385,153, issued to England on May 28, 1968, disclosed specially located frets to adjust to the frame speed of a television receiver. U.S. Pat. No. 4,061,071 issued to Cameron on Dec. 6, 1977 disclosed a stroboscopic tuning device that includes a housing whereby strings to be tuned are observed through a slot in the housing. U.S. Pat. No. 4,335,642, issued to Pogoda on Jun. 22, 1982, disclosed illumination with a monochromatic stroboscopic light source and viewing through a filter of the same color. U.S. Pat. No. 4,365,537, issued to Pogoda on Dec. 28, 1982, disclosed a strobe light held in the hand so as to shine on a vibrating string.
To maintain accuracy of tuning, the existing devices employ various means of generating accurate reference frequencies. Quartz crystal oscillator circuits are commonly used to generate a highly accurate base frequency which is divided to close approximations of the equal tempered scale with frequency divider circuits.
However the above devices in the third category have not achieved commercial success and all have some disadvantage which appears to have prevented commercial acceptance. Thus the device of England is inconvenient if a television receiver is not at hand so that this device is impractical even if it is technically viable.
Other existing devices in the third category suffer from difficulty of observation due to low perceived strobe light intensities relative to interfering ambient lighting conditions. Observing reflected light is particularly problematic and Pogoda, in various patents, finds it necessary to use lenses or filters or to electronically simulate a string's vibration to enhance the strobe effect. Without discussion of its advantages, Cameron employs a better method which is, not to rely solely on reflected light, but to position the strobe light source behind the string so that some of the light travels directly from the source to the eye. Nevertheless, because short pulses of strobe light are employed, overall perceived intensity is low and Cameron finds it necessary to use a housing to shield the string from ambient light.
Existing devices in the third category do not provide an indication of whether a string is sharp or flat, only that a string is in tune or not.
Electronically generating standard musical frequencies presents a problem which is not satisfactorily resolved in existing designs. In particular, the equal tempered musical scale is based on irrational numbers. For example, in the equal tempered scale, B has a frequency of 246.94165 which in England's preferred embodiment is approximated as 247.5. Whitaker and Peterson use frequency divider circuits to approximate desired musical frequencies. Scott recognizes the inaccuracy of divider circuits and provides a solution which uses a shift register clocked by a microprocessor implementing a software delay algorithm, but this scheme is complicated and requires considerable programming effort and expertise to implement even the single desired frequency as described.